Magnetic and magnetocaloric properties of HoCrO3 tuned by selective rare-earth doping

Abstract

Rare-earth chromites (RCrO 3 ) are an important sub-class of functional materials with interesting magnetic, electrical, and catalytic properties that make them promising for various applications. Here, we report comparisons on the structural and magnetic properties of ) ions at the A-site with ionic radius smaller (or larger) than that of Ho 3+ ion. The structural properties of the samples were characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy carried out at ambient. The band gaps of the three samples were determined by analyzing their UV-Vis spectra. Magnetic studies carried out from 5K to 300 K in magnetic fields up to 70 kOe show that the Néel temperature ( , where Cr 3+ ions order)increases with an increase in the average A-site (R-site) ionic radius, tolerance factor, and Cr1-O1-Cr1 bond angle, but decreases with an increase in the orthorhombic strain factor. In addition, the application of external hydrostatic pressure was found to enhance of HoCrO 3 , similar to the effect observed by doping HoCrO 3 with Gd 3+ ions. These changes in with A-site doping and hydrostatic pressure are related to changes in Cr 3+ -Cr 3+ exchange coupling resulting from changes in the Cr1-O1-Cr1 bond angle and Cr1-O1 bond lengths respectively. Temperature dependent paramagnetic susceptibility data of the samples was fitted to the modified CurieWeiss law that included the Dzyloshinskii-Moriya interaction. Isothermal magnetization data showed that the magnetic behavior of the samples changes from canted antiferromagnetism at low temperatures to paramagnetism at higher temperatures. The large magneto-caloric entropy change was observed in HoCrO 3 which was enhanced by Gd doping but lowered by Tm doping showing its tunability by A-site doping. Correlation between magneto-electric properties and magnetization is discussed.2

Intrinsic structural distortion and exchange interactions in SmFexCr1−xO3 compounds

“…Such tilting controls both the magnetic superexchange, J, and the orbital overlap between B and O ions, which thus determines the magnetic ordering temperature and the conductivity. [4][5][6] It has been widely accepted that the B-O-B bond angle (B ¼ transition metal), which is reduced from 180 due to the cooperative octahedral-site rotations in the orthorhombic perovskite, is a major factor in determining the B-O-B superexchange interaction. The empirical relationship between the superexchange coupling J and the superexchange angle for the RFeO 3 family has been reported from J $ cosq (ref.…”

Observation of magnetization reversal behavior in Sm0.9Gd0.1Cr0.85Mn0.15O3 orthochromites

“…The magnetic properties of orthochromites significantly depend upon R avg , and T N decreases with decreasing R avg . 31,32 Below T N in FC mode (under H = 50 Oe applied field) magnetization increases with decreasing temperature. It attains maximum values M max ∼ 0.081 emu/g with a positive polarity at the peak temperature T peak ∼ 147 K. On further cooling, magnetization continuously decreases.…”

Low-Temperature Magnetic and Magnetocaloric Properties of Manganese-Substituted Gd0.5Er0.5CrO3 Orthochromites

“…As far as the magnetic properties of various perovskite materials are concerned, rare-earth orthochromites RCrO 3 (R = rare-earth ion) exhibit interesting magnetic properties viz. exchange bias [5], spin reorientation [6], magnetization reversal [7][8][9] and magnetocaloric effect (MCE) [10][11][12][13]. It is now a well-established fact that there are three types of magnetic interactions, namely Cr 3+ -Cr 3+ , Cr 3+ -R 3+ and R 3+ -R 3+ , in RCrO 3 materials, which govern their distinct magnetic properties in different temperature ranges [5].…”

“…The negative magnetization occurs due to the antiparallel coupling between the Cr 3+ moments and rare-earth ion moments [14]. Since the last decade, researchers have also been exploring these materials for their usefulness as a low-temperature refrigerant employing the magnetocaloric effect, which is measured in terms of magnetic entropy change and relative cooling power [10][11][12][13][15][16][17][18][19][20]. Magnetic refrigeration involving solid materials is a cooling technology that is more efficient, inexpensive, safer and more environmentally friendly than the conventional vapor-compression-based technology.…”